Such measurement devices are used, for example, for object recording and data collection for Geographic Information Systems (GIS), to determine coordinates of remote objects. Such measurement devices can also be designed as portable aiming devices, in particular for determining coordinates of military target objects, such as that described, for example, in U.S. Pat. No. 7,325,320 B2.
Such a determination of target coordinates requires the relative coordinates between the measuring device and the target object. For this purpose, the target device is aimed at the target object and the azimuthal and the zenithal alignment of the target device relative to earth are then determined. The angular values determined can then be provided, together with a typical accuracy value for each one, on a data interface of the aiming device for transmission to a firing control device. Using a firing unit, a firing action can then be applied by the firing control device into an area associated with the transmitted target coordinates.
In regard to the achievable accuracy of the target coordinates to be determined, the magnetic compass is the critical component. Due to the transmitted accuracy value of the azimuthal alignment, it is possible on the one hand to assess the effect of a firing action to be applied to the target object and on the other hand, the likelihood of collateral damage. In the case of a significant deviation between the actual and the specified typical accuracy value, this assessment can be wrong.
Even with an electronic magnetic compass it is still advisable to exercise great caution when determining actual azimuthal alignments, although the components of the magnetic and gravitational field as such are measurable with sufficient accuracy. It is also now possible, as disclosed in U.S. Pat. No. 4,949,089, to take into account the declination of the Earth's magnetic field from the geographic North almost automatically, using the “magnetic variation compensation” implemented in military GPS receivers. However, since in addition to the Earth's magnetic field, the carrier of the north direction information, the measured magnetic field usually comprises magnetic interference fields superimposed thereon, the azimuthal alignment relative to true geographic North can still often only be determined with a very limited accuracy and reliability, which can be a multiple of the pure device accuracy.
These magnetic interference fields comprise so-called stationary interference fields, associated with the measurement location, and device-fixed interference fields, which are attributable to electrical currents and both hard- and soft-magnetic materials of the device, in which the magnetic compass is installed.
From the prior art, a plurality of different methods are known, which make it possible to compensate for magnetic interference effects associated with magnetic compasses. As disclosed, for example, in DE 196 09 762 C1, device-fixed interference fields of a device having an electronic magnetic compass, which has sensors for the three-dimensional measurement of a magnetic and gravitational field, can be compensated for arithmetically using a vector equation when determining azimuthal alignments of the device. The parameters of the vector equation must first be determined by means of an optimization method. This optimization method is based on the values of a more or less rigidly defined sequence of measurements of the magnetic and gravitational field at a measurement site. In this case, the device is differently aligned in space during each of these measurements. In this way, however, stationary magnetic interference fields can neither be compensated nor detected at the measurement site.
A generic optoelectronic measuring device having a magnetic compass and a compensation functionality for this is described, for example, in US 2015/0012234 A1.
In order to at least reduce, or preferably eliminate entirely, magnetic interference effects, compensation is essential. Different compensation options exist for different sources of interference. If the magnetic characteristics of a device with a built-in magnetic compass change after compensation has already been applied, then a new compensation must necessarily be performed.
Often, however, the problem arises that the user does not perform the compensation that is actually necessary, thereby reducing the accuracy of the compass. The omission of the repeated compensation then results either from lack of time, from a lack of knowledge on the part of the particular user that a further compensation is necessary, or—since the procedure is often regarded as cumbersome—from convenience. In order to ensure the reliability of the measurements even under time pressure or with less experienced users, it would therefore be beneficial if the number of compensations to be performed could be reduced, and/or if after an initial compensation the user would not need to perform another compensation, simply because the magnetic state of the device was changed.
In the European patent application with the application number EP 16171143.7, a compensation functionality for a digital magnetic compass (DMC) of a generic optoelectronic measuring device having a plurality of hard-magnetic operating states is described. But if the measuring device is not, or not only, used in a hands-free manner, but is or can be mounted on another device instead, which also generates a device-fixed interference field or is even subject to soft-magnetic changes depending on its state, which influence the magnetic compass, the method described in EP 16171143.7 is only conditionally applicable.
If a user has such a measuring device that can be used in a plurality of different operating states, for example in one state for visual observation and one state for observation in infra-red light, and if the device is additionally to be used in two different ways independently of these operating states, that is to say, both hands-free and mounted on another device, then up to now the user has had to carry out a compensation for each relevant operating state and for each type of use and to save the parameters for later use. In the case of two operating states and two types of use, this means four compensations.
The other device may, in particular, also be a firearm. In this case, for example, due to loading or unloading or else repeatedly firing the weapon (temperature change, shock) magnetic changes can occur. The compensation would have to be repeated as often as necessary.